National Airport or as it is now known Reagan National Airport is the most convenient of the three local airports in the Washington/Baltimore area. With direct access to the Metro (subway system), you can get to downtown Washington within 30 minutes or less.
Inside, National offers a clean and inviting space that is very well lit and at some points has ceiling to floor glass panes, which offer a striking view of the jet ways. The airport is actually located across the Potomac River, in Virginia, but is close enough to DC to be considered a Washington airport. Unfortunately, due to the easy access, flights to and from this airport are priced higher then if you were to fly from Dulles (also in Virginia) or BWI (in Maryland).
There is no link for Baltimore-Washington International Airport (BWI) so I figure I will include a bit about it over here. This is a fast-improving airport that offers mostly domestic flights, but also includes non-stop service to London, Reykjavik, Cancun, Toronto, Bermuda and various Caribbean destinations. Amenities at the airport are standard by US standards so no surprises here. Clean and comfortable space.
Travel to and from BWI is the only drawback since there is no direct, mass transit shuttle service as yet. You either have to take a train and change or take the Metro to Greenbelt station where you transfer to a shuttle bus (for 3 dollars) and ride straight to the airport. It is not recommended to take a taxi to BWI, unless you can afford the high amount. Dedicated, private van services to all three airports can cost from 15 dollars and upwards, depending on how far you are.
I hope these reviews for National and BWI have been helpful to you if you ever visit the Baltimore-Washington area.